The proposed dam involves a massive 204 m high dam on river Yamuna at a place called Lakhwar upstream of the Dehradun town with storage capacity of 580 Million Cubic meters, submergence area of 1385.2 ha, including 868.08 ha forest land, at least 50 villages to be affected by submergence of land in the upstream, many more in the downstream area.
This site is just about 120 km downstream of the river’s origins from the holy shrine of Yamunotri. The composite project involves, in addition to the Lakhwar dam with 300 MW underground power house, another 86 m high Vyasi dam with 2.7 km long tunnel and 120 MW underground power house and a barrage at Katapathar.
It is well known that Himalayas are the world’s youngest and hence the most restless mountain systems. At an age of 45 million years as compared to some 400 million years of Aravalis, it is a baby of the mountain chains. Young folded and still rising, Himalayas are more tectonically active than most mountains.
The evolution of Himalayas is as a result of repeated deformation of the sedimentary successions accumulated in the Tethys sea. Topographically, the highest and in age, the youngest, the Himalaya is characterized by its distinctive structural architecture and unique sedimentary and tectonic history.
The following four major litho-tectonic phyiographic zones have been recognized (Valdhiya, 1980) which are separated from each other by major faults and thrusts:
- Outer Himalayan Siwalik belt
- Lesser Himalaya
- Great Himalaya
- Tethys Himalaya
The majority of the hydro-electric projects, (including Lakhwa Vyasi Dam project) are located in the Lesser Himalaya due to deep dissected valleys, favourable for high dams, big reservoirs and availability of the water heads for power generation. The lesser Himalaya with elevation ranging from 1500 m to 3000 m has strongly folded and multiply thrusted sedimentary and metamorphic rocks.
From the structural map of Uttarakhand showing the locations of dams and the terrain–defining thrusts and faults, it becomes obvious that presumably three factors weighed heavily in the siting of dams in the state, namely
- Narrowness of the valleys;
- Adequate water discharge in rivers and
- Head of water requisite for turning turbines of generators
It is also quite apparent that the structural lay out (particularly related to faults and thrusts in the areas chosen) and the seismicity of the region were not taken into consideration.
Vulnerable location of the Lakhwar Vyasi Dam sites
The Lakhwar Vyasi dam sites are located in Lesser Himalayas, within what is termed the main central thrust (MCT) zone.
As the northward moving Peninsular India presses on, the Lesser Himalaya rock assemblages are compressed and are pushed under the huge pile of the Great Himalayan rocks, the latter riding southwards onto and over the Lesser Himalaya. The movement has been going on since the MCT was formed 20-22 million years ago. This movement is not continual but intermittent, rather episodic.
The development of hydroelectric projects not only entails excavations for the head race dams and associated coffer dams, diversion tunnels, main tunnels for carrying water to turbines, and multitudes of adits, but also for the network of roads, for residential colonies for work force, and for power generators. Obviously a dam site – no matter if it just a small one – is excessively subject to tampering with natural balance in a zone of very weakened rocks.
The fact that rocks in the vicinity of Lakhwar Vyasi dam sites are extremely weak are evidenced by instances of frequent land slides recorded and reported in the region.
Reactivation of the active thrusts is bound to impact the stability of the engineering structures. One of the impacts could be the displacement or disruption of the structures (dam damage and even break) due to sudden release of stress that the thrust movements entail. The effects on the tunnels associated with dams would be far more severe – there would be disruption or offsetting of tunnel, roof collapse, sudden onrush of interstitial groundwater with crushed material, and severe damage to tunnel lining.
Here it may be mentioned that as shown in the map of MCT Zone, the dam sites of Lakhwar Vyasi project are within the southern active zone of instability as is shown in the map in Valdhiya, 2014.
It is unfortunate that the above known vulnerable state of the Lakhwar Vyasi dam sites has been totally ignored and public security and safety compromised through so called clearances by various authorities.
Report prepared by
YAMUNA JIYE ABHIYAAN
Yamuna Jiye Abhiyaan emerged in 2007 as a movement that works to connect citizens to the Yamuna river and raise awareness about its cultural and ecological significance. The group is active in generating conversations about the impacts of industry, as well as hosting events- such as river walks, bottom-up floodplain mapping, and other workshops- that actively engage citizens in connecting with and protecting the river and its floodplain. Follow along with their incredible efforts here.